1. Field of the Invention
This invention relates to jack assemblies especially useful for raising one side of four wheel vehicles such as cars or trucks and is particularly useful for raising smaller vehicles of the unibody type without damage to the body or frame defining components of the vehicle.
Automobiles and trucks of the unibody type which do not have a separate, monolithic frame serving to provide lift points that distribute stresses imposed thereon over a large area of the vehicle present jacking problems because portions of the body function as frame defining elements which can be damaged if localized forces are applied thereto. In the case where individual, independent frames are provided upon which the vehicle body rests and is secured thereto may often be jacked up by applying a force to bumpers at opposite ends of the vehicle by virtue of the fact that the bumpers are connected directly to opposed extremities of the frame. However, as indicated, unibody vehicles do not offer these jacking points whereby one or more wheels may be lifted off the ground either to change tires or for working on the underside of the vehicle. So called "world" class automobiles now being manufactured and distributed on a worldwide basis are for the most part of the unibody type wherein elevation of a part thereof for tire changing or maintenance purposes using a portable lift as contrasted with a conventional in place, all vehicle floor hoist, must be accomplished from the side of the vehicle as the latter is tilted to raise both wheels on the one side of the vehicle off of the ground while the two remaining ground engaging wheels along with a suitable jack assembly serve as supports for the car or truck. The side rocker panels of these vehicles merge into and are joined to the floor member of the vehicle which is suitably reinforced to act as the central "frame" of the automobile or truck. If a jack is placed under the zone of merger of the rocker member with the floor panel, there is a tendency for the localized forces applied thereto to deflect and bend the metal thereby causing permanent damage to the vehicle. Although some manufacturers provide spaced, outwardly directed, open end tubes for receiving jack extensions which may be telescoped into the tubes for effecting a lifting force thereon, this requires special jacks, the vehicle can be lifted only at particular points along the length thereof, and a jack of the required type is often times not available since the jack receiving tubes may vary from vehicle to vehicle.
2. Description of the Prior Art
As indicated, jacks are known for lifting unibody four wheel vehicles such as cars or trucks wherein an extension is adapted to be telescopically received within a suitable sleeve provided therefor which is a permanent part of the vehicle along the length of the rocker panels thereon. The actual jack assemblies are generally of the ratchet type wherein reciprocation of a operating arm causes a toggle pawl and dog unit to alternately engage the rack of the jack and lift the same while a dog then moves into a rack tooth to hold the rack in an elevated position as the lever is returned to its initial position to allow another bite to be taken on the rack. These jacks are not suitable for lifting the vehicle other than at the prescribed points along the length of the rocker panels where the extensions on the jack can be suitably received in special sleeves therefore.
Bumper jacks are not suitable alternatives for many four wheel unibody vehicles because the bumpers are not attached to a one piece frame which causes the lifting forces to be imposed on the frame itself before being transmitted to the body resting thereon.
The assignee of this application was issued U.S. Pat. No. 3,780,987 for lifting heavy equipment such as forklift trucks wherein one of the lifting arms of a scissors arrangement has a fulcrum point on the ground so that the extension means moves toward and away from the fulcrum point during raising and lowering of an object carried by the lift arm of the assembly, but this jack is not adapted for raising world class cars or the like of unibody design.
Furthermore, during the lifting sequence, the scissors which engages the load to raise the same, moves in one direction of rotation through a controlled arc, while the other scissors arm of the linkage moves through a rotational arc in the opposite direction. A design that does not have this complexity of components and operation is inherently less costly.